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What are the key sensory systems?
Sight
Touch
Smell
Hearing
What are the three types of neurones?
Sensory Neurones
Motor Neurones
Relay Neurones
Draw the structure of a sensory neuron with labels
Draw the structure of a motor neuron with labels
Draw a relay neuron with labels
What does a sensory neurone do?
Transport electrical impulse from receptors to CNC
What does a motor neurone do?
Transport an electrical impulse from the CNC to an effector
What does a relay neurone do?
Process signals from multiple receptors
What components make up; the CNS (Central Nervous System)
Brain and Spinal Cord
What components make up the PNS (Peripherary Nervous system)
Nerves around the body
What are the key proteins in nerve impulses?
Na⁺ / K⁺ Pumps
Voltage gated K⁺ Channel Proteins
Voltage gated Na⁺ Channel Proteins
Sensory Receptor Na⁺ Channel Proteins
What is the value of resting potential?
-70mV
What happens at resting potential?
The Na⁺ And K⁺ Pump actively transports Na⁺ And K⁺ through the membrane in a 3:2 ratio to maintain -70mV
What ratio are Na and K ions pumped through the membrane
3:2
What happens during a generator potential?
A stimulus opens the gate to the Na⁺ Sensory Receptor Proteins
This allows Na⁺ to move in via facilitated diffusion, increasing the charge to -55mV
This starts to depolarise the membrane
Why is it important that -55mV is reached during the generator potential?
If this charge is not reached, the gates shut, and nerve returns to resting potential at -70mV
What value is an action potential?
+40mV
What happens to generate an action potential?
Na⁺ Voltage Gated channel Proteins open at -55mV, causing more Na⁺ to diffuse through
This is a positive feedback process as it increases depolarisation
40mV is reached
What happens during repolarisation?
K⁺ Voltage gates open at 40mV and Na⁺ close, causing K⁺ To flood out of the membrane, drastically decreasing the potential difference to below 70mV.
This is hyper-polarisation
Once the potential difference reaches below 70mV, the K⁺ voltage gated channel proteins shut, allowing the membrane to stabilise to 70mV.
Label this graph with the labels:
Resting Potential
Generation Potential
Action Potential
Hyperpolarisation
What is a nerve impulse?
Transmission of an action potential along an action
What is the other name for a nerve impulse?
Wave of depolarisation
What is the movement of an action potential known as?
A local circuit
Where do the Na⁺ Ions travel to, and how>
They move towards the negative region in the axon down a concentration gradient
What happens when the threshold potential is reached, in terms of Na⁺ Movement
The ions will diffuse along the axon to the next resting region once the action potential is generated
What is the refractory period?
This is the time when a new action potential cannot pass along the neurone
Why is there a repolarisation period? [3]
Ions must be redistributed to restore resting potential
Sodium voltage gated channels close
Another impulse cannot be generated
Why are refractory periods important? [3]
Ensures impulses are separated
This determines the maximum frequency of impulse transmission
Impulse therefore only passes in one direction, along the axon
What is the ‘all or nothing principal’
If threshold potential is reached, an action potential must occur. If threshold potential is not reached, nothing happens.
Why is the ‘all or nothing’ principal important?
It shows that action potentials are always the same size, and a large stimuli will increase the frequency, not the size, of the impulses.
What factors affect speed of conduction? [3]
Axon diameter
Temperature
Myelination
How does axon diameter affect speed of conduction, and why? [2]
An increase in diameter increases the speed
This is due to the lower resistance to flow of ions in the cytoplasm
How and why does temperature affect the speed of conduction? [4]
An increase in temperature increases the speed of conduction
This is due to ions diffusing faster
>40°C, conduction slows down
This is due to the denaturing of the transport proteins
How does myelination affect the speed of conduction, and why dopes this change it? [4]
Myelination means depolarisation can only occur at the nodes of ranvier
This is due to the fact myelin is not permeable to ions
Since action potential only occurs at the nodes of ranvier, the potential ‘jumps’ across the nodes
This is called saltory conduction
What are the advantages of saltory conduction? [2]
Longer local circuit
More energy efficient
Describe the basic structure of a pacinian corpuscle [3]
Single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule
Stretch mediated Na⁺ Channels on plasma membrane
Capillary runs along base of tissue
How does the pacinian corpuscle respond to pressure? [3]
Pressure deforms the membrane, causing stretch-mediated Na⁺ Channels to open
If influx of Na⁺ raises membrane to threshold potential, a generator potential is produced
Action potential moves along sensory neuron.
What are the additional features of a myelinated neuron? [3]
Schwann Cells
Myelin Sheath
Nodes of Ranvier
Named three processes Schwann Cells are involved in.
Electrical insulation
Phagocytosis
Nerve Regeneration
Where are myelinated neurones found in the body?
Most neurons in the central and peripheral nervous systems
Where are non-myelinated neurons found?
Group C Nerve fibres involved in transmitting secondary pain
What is the function of a synapse? [4]
Ensures action potentials only travel one way
Neurotransmitters send impulses between neurons/from neurons to effectors for excitatory or inhibitory response
Summation of sub-threshold impulses
Convergence/Divergence
What happens in the post-synaptic neuron when an action potential is transmitted between neurons
Neurotransmitters binds to specific receptor on postsynaptic membrane
Ligand-gated Na⁺ ions open
If influx raises membrane threshold potential, action potential is generated
What happens in an inhibitory synapse?
Neurotransmitters binds to and opens Cl⁻ channels on postsynaptic membrane and triggers K⁺ channels to open
Cl⁻ moves in & K⁺ moves out via facilitated diffusion
P.d becomes more negative: Hyperpolarisation occurs so no a.p
Define summation
Neurotransmitters from several sub-threshold impulses accumulates to generate action potential
What are the two types of summation
Temporal and Spatial
What is the difference between temporal and spatial summation?
Temporal: one presynaptic neuron releases neutransmitter several times in quick succession
Spatial: several presynaptic neurons release neurotransmitter at once
What happens at a synapse once an action potential arrives at the synaptic terminal? [4]
Voltage gated calcium ion channels open
There is a rapid influx of calcium ions into the presynaptic cell
Vesicles containing ACh fuse with the presynaptic membrane
ACh is released and diffuses across the synaptic cleft
What happens once ACh leaves the presynaptic neurone [4]
ACh binds with receptor proteins in the post synaptic membrane
ACh binding causes the opening of Na⁺ ion channels within the receptor proteins
There is an influx of Na⁺ into the post synaptic cell- initially at a relatively low rate
The post synaptic cell starts to become depolarised
What happens if the depolarisation of the post-synaptic cell reaches threshold potential? [3]
Voltage gated Na⁺ channels open
This causes a rapid influx of Na⁺ into the postsynaptic cell
This depolarises the postsynaptic cell even more, generating an action potential
How is ACh recycled? [4]
Acetylcholinesterase breaks down ACh into choline and acetate
Choline is transported back into the presynaptic cell
Choline combines with Acetylcholine CoA forming ACh, which is repackaged into vesicles
This ACh resynthesis requires ATP from mitochondria in synaptic terminal
Define convergence and divergence
Convergence: Multiple inputs, one output
Divergence:One input, multiple outputs
Note 
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